This invention relates to stripping compositions for stripping hardened photolacquers from etched semi-conductors and integrated circuits and to a stripping process employing them.
In the production of semi-conductors and integrated circuits by controlled etching, the portion of the substrate which is not to be etched is, as a rule, protected by a layer of a hardened photolacquer. After the etching is completed, this etching mask must then be removed from the substrate. Stripping agents, also called strippers, are used to strip off the lacquer layer as quickly as possible and without mechanical stress to the substrate. They must be substantially free from impurities in order to avoid undesired doping effects on the substrate. Such stripping agents conventionally are a mixture of one or more surface-active compounds, at least one phenolic compound and one or more chlorinated hydrocarbons. For example, in U.S. Pat. No. 3,582,401, strippers are disclosed which consist of an arylsulphonic acid of the general formula: ##STR1## WHEREIN M IS 0, 1 OR 2; AT LEAST ONE PHENOLIC COMPONENT, SUCH AS; FOR EXAMPLE, PHENOL, A CRESOL, A XYLENOL OR A HALOPHENOL; AND AT LEAST ONE NON-AQUEOUS, HALOGENATED DILUENT WITH A BOILING POINT ABOVE 75.degree. C., for example, carbon tetrachloride, trichloroethylene, tetrachloroethylene or o-dichlorobenzene. Similar preparations containing a long-chained alkylbenzenesulfonic acids as the surface-active agent are also commercially available.
However, these stripping agents for photolacquers possess several disadvantages which make their use difficult. One in particular is the toxicity of the phenol and chlorinated hydrocarbon components. To avoid damage to the health by these substances in use, laborious and expensive preventative measures are necessary.
A further disadvantage of the known above-described strippers is seen in their use to remove photolacquer layers which have been post-hardened for a comparatively long time at elevated temperatures. For the satisfactory removal of such etch masks, the conventional stripping agents are heated to a temperature of above 75.degree. C., preferably about 100.degree. C. At these temperatures, the solvents in the known strippers are very volatile, causing clear weight losses of the stripping agent bath in a comparatively short time, which leads to a loss in efficiency. To compensate for these losses, the bath must be supplemented at short intervals of time, frequently every 30-60 minutes, with fresh stripping agent.
It is an object of this invention to provide stripping agents for photolacquers which do not possess these disadvantages or do so to a considerably reduced extent.
It has now been found that one obtains a practically non-toxic, effective stripper with substantially reduced volatility when one dissolves 20-50 weight percent of an alkylbenzenesulfonic acid with 12-20 carbon-atoms in 80-50 weight percent of a chlorine-free, high boiling hydrocarbon.